Breathable gelatin films with saline-triggered adhesion for wireless sleep and cardiac monitoring

Robust, long-term electrophysiological monitoring demands epidermal electrodes that breathe like skin, adhere to demand, and survive the repetitive strains of daily life. Here, we present a 2.4 μm-thick, transparent, and gas-permeable epidermal electrode that adheres to human skin upon brief wetting with saline solution. The electrode is fabricated through a simple, scalable method using a gelatin matrix composed of gelatin, glycerol, citric acid, and water, reinforced by an electrospun polyurethane nanomesh. This construction yields an interfacial adhesion energy of 1.7 mJ cm^-2 and excellent breathability with a water vapor transmission rate of 1339.3 g m^-2 day^-1. The film withstands more than 1500 cycles of 60 % uniaxial strain and still exhibits an adhesion energy of 0.8 mJ cm^-2 after 48 h of skin attachment. The skin-electrode interface maintains a low contact impedance of 36.7 kΩ at 100 Hz even after 48 h of continuous wear. These properties enable stable and high-fidelity recording of electroencephalogram, electromyogram, and continuous electrocardiogram signals for over 36 h under daily activities, including lab work, commute, meal, nap/sleep, and desk work. The electrode performance remains consistent even after 30 days of ambient storage. We further demonstrate wireless electroencephalogram and electrocardiogram signals acquisition during one full night of sleep, enabling accurate and automatic sleep stage classification based on electroencephalogram spectral features and heart rate dynamics. Together, these results establish the ultrathin gelatin film as a practical platform for real-world, long-term electrophysiological monitoring and point toward its broader use in personalized healthcare wearables.